Clinicopathological features of hepatoid adenocarcinoma of the stomach: A multicenter retrospective study

Abstract Background Hepatoid adenocarcinoma of the stomach (HAS) is a rare and aggressive subtype of gastric cancer (GC), accounting for less than 1% of all cases. It is characterized by frequent liver metastasis recurrence and a poorer prognosis than conventional GC. However, established treatment guidelines for HAS are currently not available.In this report, we present the results of a clinicopathological study of 19 patients diagnosed with HAS, including seven patients with liver metastasis, conducted by the Hiroshima Surgical Study Group of Clinical Oncology (HiSCO) between 2016 and 2018. Aims The aim of the study was to retrospectively observe the outcomes of HAS with gastrectomy and hepatectomy for liver metastasis and determine relevant prognostic factor. We also examined the criteria and outcomes of hepatectomy for liver metastasis and aimed to suggest the optimal treatment for HAS, including chemotherapy. Methods and Results A total of 2147 patients underwent gastrectomy for GC at HiSCO‐affiliated institutions during the study period; 19 patients, all male with a mean age of 70.9 years, were diagnosed with HAS by hematoxylin‐eosin and immunohistochemical staining. Patients underwent gastrectomy at varying pathological stages: six at Stage I, three at Stage II, seven at Stage III, and three at Stage IV. Ten patients received postoperative chemotherapy and the 5‐year survival rate was 67.7% after gastrectomy. Among the seven patients with pre or postoperative liver metastasis, five patients underwent hepatectomy. Although one patient had recurrence, the 3‐year survival rate was 100% after hepatectomy. Conclusion Contrary to previous reports suggesting a 3‐year survival rate of approximmately 30% for HAS, our findings indicate that the prognosis for HAS may not be as poor as reported previously. This study contributes valuable insights into the management and potential treatment strategies for HAS.

67.7% after gastrectomy.Among the seven patients with pre or postoperative liver metastasis, five patients underwent hepatectomy.Although one patient had recurrence, the 3-year survival rate was 100% after hepatectomy.
Conclusion: Contrary to previous reports suggesting a 3-year survival rate of approximmately 30% for HAS, our findings indicate that the prognosis for HAS may not be as poor as reported previously.This study contributes valuable insights into the management and potential treatment strategies for HAS.

| INTRODUCTION
Hepatoid adenocarcinoma (HAC) is a rare histologic subtype of hepatocellular carcinoma that has been identified in various organs, including the stomach, ovaries, renal pelvis, papilla of Vater, lungs, and pancreas. 1,2HAC is defined as adenocarcinoma of extrahepatic origin with morphological features of liver cell differentiation, composed of large polygonal eosinophilic hepatocytes.When HAC occurs in the stomach, it is referred to as hepatoid adenocarcinoma of the stomach (HAS) according to the 4th edition of the World Health Organization classification of the tumors of the digestive system. 3HAS comprises a very small proportion of malignant gastric tumors and accounts for only 0.3% of all gastric adenocarcinoma cases. 4,5S is tumor tissue consisting of large eosinophilic cells exhibiting trabeculae separated by sinusoidal vascular channels in hematoxylin and eosin (H.E) staining.Typically, it presents with high levels of alpha-fetoprotein (AFP) 6,7 and can be confirmed by several immunohistochemical markers, such as AFP, Glypican-3, Sal-like protein 4, and Hep-Par 1.This subtype of gastric cancer (GC) frequently tends to present with liver metastases and carries a poor prognosis.The literature reports that patients with HAS have an average survival period of 10-18 months, with 1-, 3-, and 5-year survival rates ranging from 30% to 37.5%, 7% to 13%, and 8.3% to 9%, respectively. 8rrently, the mechanisms underlying the development and progression of HAS remain unknown, and no specific guidelines for HAS treatment exist.The surgical procedures and chemotherapy used for treating conventional GCs have been applied to HAS.However, HAS has a higher rate of liver metastasis (35%-76%) than peritoneal dissemination recurrence, 9,10 and the establishment of an effective treatment modality for liver metastasis would improve the poor prognosis.
In this report, we present the results of a clinicopathological study of 19 patients diagnosed with HAS, including seven patients with liver metastasis, conducted by the Hiroshima Surgical Study Group of Clinical Oncology (HiSCO).This study aimed to retrospectively observe the outcomes of HAS with gastrectomy and hepatectomy for liver metastasis and determine relevant prognostic factor.We also examined the criteria and outcomes of hepatectomy for liver metastasis and aimed to suggest the optimal treatment for HAS including chemotherapy.

| Patients and diagnosis of HAS
Between January 2016 and December 2018, a total of 2147 patients underwent gastrectomy for GC at 14 HiSCO institutions.Among these patients, 19 (0.88%) showed the following features: large, irregular cancer cells with abundant cytoplasm, that exhibited pale eosin staining and a medullary or cable structure, formed by fibrous tissues and a rich blood supply as observed with H.E staining and positive immunohistochemical staining for AFP.These were then diagnosed as HAS by pathologists at each institution (Figure 1) according to the literature. 3,11Clinical and pathological data for all 19 patients were extracted from medical records.

| Diagnosis of liver metastasis and criteria for hepatectomy
Among the 19 patients, seven had liver metastases; five underwent hepatectomy, while two did not.Two of the five patients had liver metastases at the time of GC diagnosis: one underwent simultaneous gastrectomy and hepatectomy, and the other underwent hepatectomy followed by gastrectomy.Three of the five patients experienced liver metastasis recurrence after gastrectomy and subsequently underwent hepatectomy (Figure 1).The liver metastasis was diagnosed by images of computed tomography (CT) and magnetic resonance imaging (MRI) or positron emission tomography CT (PET-CT).Liver metastases appeared as lowdensity areas in the portal vein contrast phase in CT and the hepatocyte contrast phase in MRI, and they appeared distinct from primary liver cancer.
The criteria for hepatectomy were as follows: preserved hepatic function (Child-Pugh A/B), no HAS metastasis to organs other than the liver, three or fewer tumor units, and portal vein invasion up to the first bifurcation, accordance with the Japanese guidelines for liver cancer treatment. 12Age and tumor diameter were not included in the criteria.

| Assessment for adverse events of chemotherapy
Adverse events to chemotherapy administration were evaluated using the Common Terminology Criteria for Adverse Events (CTCAE) v4.0.

| Statistical analysis
Survival rates were estimated by Kaplan-Meier survival curves, employing EZR (Saitama Medical Centre, Jichi Medical University, Saitama, Japan), a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria).Specifically, EZR is a modified version of the R commander designed to incorporate statistical functions frequently used in biostatistics. 13Statistical significance was defined at the level of p < .05.

| Patient characteristics
A summary of the 19 cases diagnosed as HAS is presented in Table 1.

| Cases with chemotherapy
Adjuvant chemotherapy for pStage II or III was administered in seven cases and chemotherapy for pStage IV was administered in three cases (Table 2).In pStage II and III patients, two patients received capecitabine with oxaliplatin (CapeOX) according to the CLASSIC trial protocol as adjuvant chemotherapy. 15One completed the course and one stopped oxaliplatin after the third course due to the adverse events of peripheral neuropathy (Grade 3 by CTCAE) and only capecitabine was continued.Four patients received S1 according to the ACTS-GC protocol, 16 of whom treatment was completed in three patients, but one patient stopped after the second course due to the adverse events of skin disorder (Grade 2 by CTCAE).One patient received S1 with docetaxel (DS) according to the JACCRO GC-07 protocol 17 and the treatment was completed.In pStage IV, all three patients received S1, two patients were shifted to second-line treatment because of recurrence and died due to disease progression.One patient is still on S1 without recurrence.

| Overall survival rate after gastrectomy and recurrence rate
The overall survival rate after gastrectomy was 100% at 1 year, 78.9% at 3 years, and 67.7% at 5 years (Figure 2).All patients were followed up at the institution where the surgery was performed.The median follow-up duration was 4.9 (range 1.1-6.9)years for all patients.
Among the six patients in pStage I, two exhibited recurrence (33.3%), and among the 13 patients in pStage II, III, IV, five exhibited recurrence (38.5%).There was no statistical difference in recurrence rate between the two groups (p = 1).The 5-year survival rate of patients in pStage I was 44.4% and pStage II, III, IV was 76.9% ( p = .205)(Figure 3).Two patients with pStage I died during the observation period.The one was pathologically diagnosed with the Intestinal type, T1b, N1, Ly1a, V1c and died from jaundice and liver failure due to multiple liver metastases 1 year after gastrectomy.The other patient was died of respiratory failure due to exacerbation of emphysema without recurrence of HAS.

| Cases and survival rate with hepatectomy and efficacy of chemotherapy for liver metastasis
Of the 19 cases, liver metastasis was detected in seven cases on CT, MRI, or PET-CT, of which hepatectomy was performed in five cases and two cases were deemed unresectable (Figure 1).F I G U R E 2 Overall survival after gastrectomy: 1-year survival rate 100%, 3-year survival rate 78.9%, and 5-year survival rate 67.7%.
In pStage I, two patients with liver metastasis were detected, 1 patient could not be treated as resectable and one patient underwent CapeOX treatment followed by hepatectomy.In pStage II, two patients with liver metastasis were detected, of which one was not resectable, and one underwent hepatectomy after CapeOX treatment.
In pStage III, one patient with liver metastasis was detected, and the patient underwent hepatectomy after CapeOX treatment.In pStage IV, two patients with liver metastasis at the time of diagnosis of GC underwent hepatectomy after chemotherapy (Table 3).
According to Becker's criteria, tumor regression grade (TRG) is determined on resected specimens of liver metastases and GC by pathologists at each institution. 18,19In all cases, chemotherapy resulted in a pathologically effective response.The 3-year survival rate for the five cases with hepatectomy was 100% (Figure 4).
The median follow-up duration was 3.5 (range 2.6-5.3)years for all patients.

| DISCUSSION
In 1985, Ishikura et al. reported the first case of HAS; the following year, they documented seven similar cases, highlighting that this tumor type primarily occurred in elderly individuals, often in the antrum, exhibited distinct hepatoid differentiation, frequently had liver metastasis, and was associated with a poor prognosis. 20Immunohistochemically, AFP is often distributed in hepatoid regions, and more is expressed by more than 90% patients, whereas it is weakly or focally positive in adenocarcinomatous areas. 5,11AFP and hepatocyte antigens can be utilized to differentiate HAS from hepatocellular and common adenocarcinoma of the stomach.
HAS is a unique subtype of GC that frequently metastasizes to the liver.To the best of our knowledge, since 2010, according to original articles on HAS, 8,9,21-27 reported cases have been from single centers (Table 4).The rate of preoperative liver metastasis of GC ranged from 2.7% to 17.6%, and postoperative liver metastasis of GC from 21.1% to 75.6%.2][23][24][25][26] However, Zhou et al. reported a relatively favorable prognosis, with 1-and 3-year survival rates of 87.9% and 82.6% after gastrectomy, respectively. 27Our study results showed that the 1-, 3-, and 5-year survival rates post-gastrectomy were 100%, 78.9%, and 67.7%, respectively, which is considered a relatively good prognosis, as reported by Zhou et al.
Various drugs, such as platinum, antimetabolites, and moleculartargeted agents, have been used for chemotherapy in prior reports, and transcatheter arterial chemoembolization or radiofrequency ablation (RFA) have been used for liver metastases, with no consensus on drug therapy. 5,28Even when limited to adjuvant chemotherapy, several agents are employed, including S1 with oxaliplatin (SOX),  F I G U R E 3 Comparison of survival rate between pStage I and II, III, and IV.There was no statistically significant difference in the 5-year survival rate between the two groups (p = .205).
cisplatin/cetuximab, and docetaxel. 9,23,26,28However, standard neoadjuvant or adjuvant chemotherapy for HAS recommended by randomized controlled trials has not yet been established and Zhou et al. reported no effect of neoadjuvant chemotherapy on HAS in a retrospective analysis. 5,29To our knowledge, there are no reports showing the efficacy of immune checkpoint inhibitors or hyperthermic intraperitoneal chemotherapy in the literature.We introduced conventional chemotherapy for GC according to the literature [15][16][17] and the result was better than reported in previous literatures.These results suggest that administering chemotherapy for GC in patients with HAS may be beneficial.
Chemotherapy is the mainstay of treatment for liver metastasis after gastrectomy and the efficacy of hepatectomy in such cases in controversial.A latest systematic review reported 1-and 3-year survival rates of 69.8% and 34.8%, respectively, after hepatectomy for liver metastases of GC. 30 In addition, in Japanese treatment guidelines, hepatectomy is weakly recommended for solitary liver metastasis without other incurable factors. 31 a retrospective study, Kinoshita et al. reported 1-, 3-, and 5-year survival rates of 77.3%, 41.9%, and 31.1%,respectively, in a multicenter of resection of 256 postoperative liver metastases from GC. 32 Moreover, Oki et al. reported 3-and 5-year survival rates of 51.4% and 42.3%, respectively, in 94 cases of postoperative liver metastases from GC treated with a combination of surgery, RFA, and microcoagulation therapy in a multicenter study. 33Unlike liver metastases from colorectal cancer, liver metastases from GC are often unresectable; therefore, the effectiveness of hepatectomy is debatable.
However, these two reports suggest that hepatectomy may be beneficial in some instances.Kinoshita     3).Since only one patient died after recurrence, these two reports might be applicable to determine prognostic factors in instances of liver metastasis resection from GC, including HAS.Moreover, liver function was favorable in the five patients who underwent resection, and chemotherapy proved effective (Table 3).To the best of our knowledge, this is the first report addressing treatment considerations and prognosis, including hepatectomy, for recurrent liver metastases following gastrectomy for HAS.In our study, unlike in previous reports, HAS exhibited a relatively favorable prognosis.These results also suggest that aggressive hepatectomy combined with chemotherapy may improve the prognosis of recurrent liver metastases if liver function is satisfactory and the tumor is resectable.However, liver metastasis was observed in six patients (31.6%) even at pStage I after gastrectomy, implying that patients with HAS should be monitored as closely as those with advanced GC.In fact, though the difference was not statistically significant, pStage I had a worse prognosis than pStage II, III, and IV (Figure 3).The introduction of adjuvant chemotherapy for pStage I cases may lead to a lower recurrence rate and improved prognosis.
This study had some limitations.There is possibility that some AFP-negative cases may harbor cases diagnosed as HAS by other immunostaining, because we focused on AFP-positive HAS cases.In addition, unlike previous reports, our results are derived from a multicenter study, and our findings cannot be generalized as a strategy due to the small number of cases.Nevertheless, our report may contribute to the selection of strategies for treating liver metastases or chemotherapy in patients with HAS.

| CONCLUSION
The results of our study suggest that HAS treatment according to the standard treatment guidelines for GC may result in an improved prognosis compared to previous reports.Moreover, pStage I cases also show a high recurrence rate; therefore the introduction of adjuvant chemotherapy and a follow-up regimen similar to that used for pStage II or higher cases are desirable.Active surgical intervention for liver metastases from HAS may improve the prognosis.
adenocarcinoma of the stomach F I G U R E 1 Flow chart of participant inclusion in the present study.
et al. identified three prognostic factors: the presence of serosal invasion of the primary tumor, two or fewer liver metastases, and a maximum tumor diameter of less than 5 cm.Oki et al. reported the following three prognostic factors: only one liver metastasis, up to N1 lymph node metastasis, and a maximum tumor diameter of less than 3 cm.Although it remains unclear whether these two reports encompass HAS cases, when applying the prognostic factors from both reports to our five cases with liver metastasis, one of the five cases T A B L E 4 Original article summaries of hepatic adenocarcinoma of the stomach since 2010.

F I G U R E 4
Overall survival after hepatectomy: 3-year survival rate of five cases was 100%.met the two prognostic factors reported by Kinoshita et al. and the two prognostic factors reported by Oki et al. (Table